1. Field of the Invention
The present invention relates to an electronic still camera and, more particularly, to high-speed continuous shooting suitable for the electronic still camera.
2. Description of the Related Art
An electronic still camera (also called the still video camera) has conventionally been provided with a continuous shooting mode, and the electronic shutter function of an image sensor such as a CCD has been utilized to increase the continuous shooting speed of the electronic still camera. As compared with a silver-salt camera, such a continuous shooting function is useful for the electronic still camera which uses an erasable and re-recordable medium.
To gain the continuous shooting speed, various proposals have been made. A primary factor which determines the continuous shooting speed is the operating time of mechanisms. The continuous shooting speed is not affected by the shutter of the electronic still camera since an electronic shutter is utilized. However, since a magnetic head is mechanically arranged, the time required to move the magnetic head influences the continuous shooting speed.
To solve the problem, it has been proposed to provide an electronic still camera having an image memory. In such an electronic still camera, image data read from an image sensor are thinned out to prepare image data having a data size reduced to 1/16 or 1/25 of the original data size, and the thus-prepared image data are stored in the image memory so that the image data are sequentially subjected to continuous shooting. A series of data which has been prepared in this manner is read from the image memory and written to a video floppy disk. At this time, since a 1V (vertical scanning) period is necessarily needed to complete a reading from the image sensor, the 1V period constitutes a primary factor which determines the continuous shooting speed.
Regarding the high-speed continuous shooting, the above-described electronic still camera has the problems described in the following paragraphs (1) to (3).
(1) Since the 1V period ( 1/60 second) is required to complete a reading from the image sensor, it is difficult to shoot a rapidly moving subject.
(2) Even while a subject is not moving, recording is performed, so that a number of useless exposures are produced.
(3) If a plurality of exposures which have been recorded as one picture are reproduced, the motion of a subject is difficult to grasp.